For example, a steam generator used for a PWR (Pressurized Water Reactor) involves a concern that radioactive water leaks from a primary side to mix in non-radioactive water on a secondary side when a side wall of a U-letter shaped heat-conducting tube incorporated therein exceeds a permissible level and thus deteriorates. For this reason, there is a known scheme in which the concern of being mixed is prevented by blocking off an end of the heat-conducting tubes involving deterioration or a possibility of deterioration.
Previously, for example, a plugging device of a tube disclosed in Patent Literature 1 includes a tubular plug shell including an open end which is open at one end and a closed end which is closed at the other end, an expander element that is incorporated in the plug shell and movably provided between the closed end and the open end, and an expansion unit including a supply source of pressurized hydraulic fluid for facilitating a movement of the expander element by introducing pressurized hydraulic fluid into the plug shell. In addition, a plugging method of a tube disclosed in Patent Literature 1 introduces pressurized hydraulic fluid into a plug shell using the plugging device described above to expand the plug shell in a radial direction, and facilitates a movement of an expander element between a closed end and an open end of the plug shell.
In the device of Patent Literature 1 described above, the inside of a hollow of the plug shell is surrounded by a tapered inner wall surface. The inner wall surface has a circular cross-sectional surface in a traverse direction with respect to an axis line in a longitudinal direction of the plug shell. In addition, the inner wall surface converges so that the open end of the plug shell is a minimum area, and expands so that the closed end of the plug shell is a maximum area. On the other hand, the expander element includes a conical main body in a shape of a cork, and the conical taper is substantially equally formed with the taper of the inner wall surface of the plug shell. In the method of Patent Literature 1 described above, a threaded portion of a front end of a draw bar member in the expansion unit is screwed with a threaded hole of a main body in the expander element, and the expander element is moved from the closed end to the open end within the plug shell by the expansion unit. In this way, the taper of the expander element comes into contact with the taper of the plug shell, and the plug shell is pushed outside in a radial direction by a wedge effect, thereby causing the plug shell to stick to the inner wall surface of the heat-conducting tubes and block off the heat-conducting tubes.